Are there any historically known examples (from memoirs, letters, testimony etc...) of US Presidents discussing classified things with their spouses/lovers?
This article by CNN lists out examples of Presidents who discussed classified things with their wives:
Jacqueline Kennedy received the intelligence community's highly classified "Weekly Intelligence Summary" from October 1962 till the summer of 1963.
Lyndon Johnson also discussed discussed policy with Lady Bird Johnson, as she noted in her diary.
Hillary Clinton was also "often provided" with classified information.
There might be other examples too, especially of Presidents in the 19th century which are harder to find, but these are the notable cases that I have occasionally heard of.